Scientists are learning more about how smoking impacts our health all the way down to our genes, and experts say they're not terribly surprised by new findings that some of the changes to a smoker's DNA appear to be permanent, lingering even decades after the smoker quits, reports NBC News. Focusing on DNA methylation, which is what happens when there are changes not to a gene's underlying code but to how the gene is activated, researchers report in the journal Circulation: Cardiovascular Genetics that smoking impacts 7,000 genes, or roughly one-third of a person's entire genome. Cigarette smoking continues to be the leading preventable cause of death globally and accounts for 6 million deaths every year.
The news isn't entirely grim. In looking at the blood samples and smoking habits of 16,000 people across 16 studies dating as far back as 1971, researchers say the vast majority of affected genes returned to normal within five years of the smoker quitting. "Your body is trying to heal itself," one says. (Another new study out of Washington University finds that quitting smoking cuts lung cancer risk in half, even for those most at risk.) But in 19 genes smoking-related changes persisted for 30 years, including the TIAM2 gene linked to lymphoma. "Smoking has such a wide array of effects, it's not especially surprising to hear its epigenetic effects," one expert tells WebMD as he ticks off a lengthy list that includes cancers, bone disease, lung disease, and heart disease. (Cigarette smoke even makes superbugs harder to kill.)